I used to be a mechanic once upon a time for an independent shop. It sounds like I'll have the minority opinion here with some caveats. That said I don't think most have bad advice in this tread. IMHO the best thing you could do is switch to conventional oil and change every 3k from the oil pan. Mose people don't want to spend the extra money and time so they do the next best thing which is every 5-6k with Synthetic. This is the next best thing.
The way it was always explained to me is that is the particulate that gets trapped in the oil that you need to get out of the system. While it's true that synthetic oil cleans better and retains is structure better than conventional, keeping the particulate matter in the oil longer is less ideal then getting it out of there sooner. If you change every 3k in 3-4 mo intervals you won't get sludge buildup that people refer to. Conventional oil also leaks past seals less then synthetic. Again, you can save some money and time if you want to do the next best thing and stick to the synthetic schedule mentioned in this tread.
As for changing the oil from the top, I'd personally never do this because the particulate falls to the bottom of the oil after the engine is at rest. If you pull it out from the top you leave that particulate at the bottom which is the point of the oil change and less ideal. Either 5-6k syn changes or 3k conventional changes will likely serve you well, but I'd caution you from changing every 10-15k like the dealership recommends. That's kind of crazy IMHO. As someone else said earlier, I think they give those recommendations for marketing purposes and the fact that they usually only have to make the car last as long as the warranty. Then they don't really care what happens to it. Talk to 3 mechanics and you'll get 3 opinions as the old saying goes
